In the art and science of painting, it is a practice to prepare a surface that is to be painted to receive paint. A surface properly prepared is more likely to produce a desirable result and remain properly painted for a long term. Preparation techniques vary depending on the material to be painted, the type of primer, stain and/or paint which will be used, the manner of application of the paint and the conditions to which the painted item will be subjected, among others.
In the past, with respect to automobiles and automobile parts, plastic played a minor role and typically could be prepared such that the plastic part was molded in the desired color. As plastic has become a more important product in the automobile industry, such items as interior and exterior doors, dashboards and other body panels and protective equipment, such as bumpers and door guards, have been made of a plastic material. Typically, exterior plastic parts, especially in modern vehicles, are painted to match or aesthetically contrast, with the body of the automobile.
In order to speed production of parts, and reduce costs, plastic parts are now typically molded in one color (such that only a single run of molding is needed for all colors offered in a vehicle model) and then painted to match the desired vehicle color. This allows for less planning and more availability of parts for all colors of a vehicle model, and typically greater numbers of color combinations to appeal to the tastes of purchasers. Further, this manner of producing parts allows an adequate supply of replacement parts for subsequent body repair needs on any color vehicle.
A problem arises, however, in producing painted parts, in that the plastic materials, used as body parts, typically must have a smooth surface in order to be acceptable. Smooth surfaces are typically not amenable to painting. Paint sprayed, or otherwise placed, on smooth surfaces, especially those with low surface energies, generally does not stick to the surface and may be peeled or chipped off, which is a highly commercially undesirable result. While various means have been provided to stem this problem, such as abrading the surface prior to painting or adding adhesives, such as epoxy, to paint, in order to get the paint to stick to the item being painted, none of these has proved effective.
It has been found that the use of a grafting material, such as those in a family of multifunctional amine-containing organic compounds, on plastic parts, which have been oxidized, allows paint to better adhere to the plastic. See, for example, U.S. Pat. No. 5,922,161 to Wu et al. (the “'161 patent”) that discloses a method of modifying or tailoring the surface of polymers and or polymer-based materials to control surface and interface chemistry and molecular structure. The '161 patent discloses a method for oxidizing the surface of a polymer and treating the surface with a grafting chemical. The content of the '161 patent is incorporated by reference into this application as if fully set forth herein.
It has been found, however, procedures which employ the use of grafting chemicals added to plastic parts which have been oxidized are typically only generally applicable to sheets of plastic. Further, there is a potential for the devices and methods used to oxidize the plastic and apply the chemicals to sheets of plastic typically do so in such manner as to cause areas of the plastic sheet to be treated more than once, because of inadvertent overlapping, wasting chemicals, causing the loss of production time and potential cohesive weakening in the over treated areas.
In one plastic sheet treating operation, a gas/air burner, having a large area with many burner ports is used. The burner device is moved over the plastic sheet, overlapping some sections of the sheet in movement. In the operation of such a system, the burner oxidizes the plastic sheet, and then a grafting chemical is sprayed onto the oxidized plastic, to prepare the plastic for further processing, such as with paint, adhesives or other coatings. The sheet is thereby made amenable to adhesion by other chemicals, including paint.
However, plastic parts typically are not made in the form of plastic sheets, especially in automobile applications. Plastic parts are generally constructed in all shapes and with undulations, indentations, openings, crevices and other contours. The use of such treatment devices and methods, as described above, are ineffective to treat the variations in modern plastic parts. Further, treatments such as dipping or spraying have been found to be ineffective, as the oxidation process cannot pre-treat the non-linear sections of the plastic part, causing the sprayed grafted material to be wasted.
Further, it has been found that the use of prior treating apparatus often cause large number of toxic chemicals to be released into the atmosphere as a result of the shot-gun approach to the treatment of plastics. This is especially the case when adhesion promoters are utilized to prepare a plastic substrate part to accept paint.
Another problem that exists in present plastic part treatment methods is that once the part is treated it is typically difficult, without sophisticated tests, to discern a difference between the treated part and an untreated part. In many instances, items that have been treated have been confused with items which have not been treated, causing a waste of materials and time in retreating, and, generally, an over weakening of the surface of the part which is re-treated.
Another problem has occurred in that in a typical system used in any field where a supply of chemicals must be mixed and propelled, there is a tendency for machinery to break down and/or need general maintenance, during a work cycle, so that it can work nominally and continuously. Typically, a chemical application system must be shut down for repair or so that chemicals or other components can be replenished or so that normal maintenance can be completed, stopping production while the system is being replenished, repaired or maintained.